Plasma-assisted method and system for treating raw syngas comprising tars

ABSTRACT

This disclosure provides a system and method for conversion of raw syngas and tars into refined syngas, while optionally minimizing the parasitic losses of the process and maximizing the usable energy density of the product syngas. The system includes a reactor including a refining chamber for refining syngas comprising one or more inlets configured to promote at least two flow zones: a central zone where syngas and air/process additives flow in a swirling pattern for mixing and combustion in the high temperature central zone; at least one peripheral zone within the reactor which forms a boundary layer of a buffering flow along the reactor walls, (b) plasma torches that inject plasma into the central zone, and (c) air injection patterns that create a recirculation zone to promotes mixing between the high temperature products at the core reaction zone of the vessel and the buffering layer, wherein in the central zone, syngas and air/process additives mixture are ignited in close proximity to the plasma arc, coming into contact with each other, concurrently, at the entrance to the reaction chamber and method of using the system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 15/543,768, entitled “PLASMA-ASSISTED METHOD AND SYSTEM FOR TREATINGRAW SYNGAS COMPRISING TARS”, which was filed Jul. 14, 2017, which is anational stage entry of PCT/CA2016/050027, entitled “PLASMA-ASSISTEDMETHOD AND SYSTEM FOR TREATING RAW SYNGAS COMPRISING TARS”, which wasfiled Jan. 13, 2016, which claims the benefits and priority of U.S.Provisional Patent Application No. 62/103,114, entitled “PLASMA-ASSISTEDMETHOD AND SYSTEM FOR TREATING RAW SYNGAS COMPRISING TARS”, which filedJan. 14, 2015. The entire contents of the aforementioned patentdocuments are incorporated by reference as part of the disclosure ofthis application.

TECHNICAL FIELD

This invention pertains to the field of syngas treatment. In particular,it relates to a plasma assisted method and system for treating rawsyngas comprising tar.

BACKGROUND

Gasification is a process that enables the conversion of carbonaceousfeedstock, such as municipal solid waste (MSW) or biomass into acombustible gas. The product gas of the gasification of MSW oftenincludes a significant amount of tar.

Prior to use, the product gas from gasification is often refined.Refinement systems include those that expose the product gas to plasma.Plasma refinement reduces the larger hydrocarbon molecules in theproduct gas to a combination of hydrogen, carbon monoxide, carbondioxide and steam, with some trace contaminants, through the processesof thermal decomposition and plasma catalysis. The hydrogen and carbonmonoxide mixture, known as synthesis gas (syngas) can be combusted in aninternal combustion engine generator(s), which converts the chemicalenergy of the syngas into electrical energy. A steam turbine generatoruses the by-product heat from combustion to produce additionalelectricity.

An efficient and reliable process of producing refined syngas cansignificantly impact the economics of waste or biomass plants.Improvements in the refinement process and related mechanisms are anongoing effort at many research facilities, in light of current interestin renewable energy, waste management and hydrogen/syngas fuels.

Companies like Advanced Plasma Power (APP), for example, have developeda two-stage thermal Gasplasma™ process to produce refined syngas, whichcan be fed directly into a gas engine for the efficient recovery ofenergy. In this process, the plasma treatment step is for both off-gasand solid residue in a single chamber and the issue with having one unitfor gas and inert treatment is in the lack of separate control of thegas/inerts treatment.

Hadidi et al. in “Plasma Catalytic Reforming of Biofuels”, Dec. 17,2003, discloses fuel reforming experiments from partial oxidation ofbiofuels, in which a calculated amount of oxygen is added in thereactor, in order to capture each carbon atom in the fuel as carbonmonoxide, thus releasing hydrogen as hydrogen molecules. The productionof plasma, by using a plasmatron reforming technology, allows for arobust and large volume reaction initiation of the fuel-air mixture. Thework describes the procedure, results and analysis of bio-fuelsreformation using low-current plasma discharges. Hadidi also discussesthe possibility of limiting the air supply to the reactor, to controlthe reaction kinetics and subsequently the composition of theireffluent.

In addition, Hadidi describes the use of a boundary layer of air toprotect the walls of the reactor from high temperatures that are presentin the core reaction zone of the reactor.

In the Hadidi process, fuel passes through a thermal plasma torch, whichhas three air inlets and the end result is that everything is convertedto plasma; mixing is only a side note to ensure having a stable plasmafield.

In some prior art systems, poor mixing of the air and syngas componentsresults in stratification of the reactant mixture within the reactorbody, thus forming dynamic regions in the reactor that are fuel-rich,fuel-lean or stoichiometric. This creates a challenge from anengineering standpoint, because it does not allow the use of a specific,static strategy for igniting the air-fuel mixture, as the mixture molefractions are constantly evolving. Subsequently, it results in anunstable flame in the reactor, leading to inconsistent temperaturesprofiles and poor tar conversion.

These aforementioned challenges reduce the tar conversion efficiency ofthe refining chamber.

Although effective at reducing tar contamination, plasma, a hightemperature medium consisting of highly reactive species, mayundesirably cause corrosion of the reactor walls.

This background information is provided for the purpose of making knowninformation believed by the applicant to be of possible relevance to thepresent invention. No admission is necessarily intended, nor should beconstrued, that any of the preceding information constitutes prior artagainst the present invention.

SUMMARY

An object of the present invention is to provide plasma-assisted methodand system for treating of raw syngas comprising tars. In accordancewith an aspect of the invention, there is provided a plasma-assistedsystem for treating raw syngas comprising tars, comprising: (a) arefining chamber for refining syngas comprising one or more inletsconfigured to promote at least two flow zones: a core reaction zonewhere syngas and air/process additives flow in a swirling pattern formixing and combustion in the high temperature central syngas flow zone;at least one peripheral zone within the reactor which forms a boundarylayer of a buffering flow along the reactor walls, (b) one or moreplasma torches that inject plasma into the core reaction zone, and (c)air injection patterns that create a recirculation zone to promotemixing between the high temperature products at the core reaction zoneof the vessel and the buffering layer; wherein in the core reactionzone, syngas and air/process additives mixture are ignited in closeproximity to the plasma arc, coming into contact with each other,concurrently, at the entrance to the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, by reference to the attached figures, wherein:

FIG. 1 illustrates one embodiment of the system detailing raw syngasinput 200 and injection of raw syngas along the internal periphery 800of the reactor chamber 500, the process air/additive input 300, plasmaapplication 400 and mixing zone 600, and the processed syngas output700.

FIG. 2 illustrates a side view of one embodiment of the systemconfigured, such that the inlet splits the raw syngas feed 309 into twovolumetric flows: 302 (central syngas flow zone) and 306 (peripheralsyngas flow zone), and feeds the syngas into the reaction chamber, whilethe process air is routed through air entrance ports 301 that areperpendicular to the chamber and tangential to the main flow. FIG. 2also shows the low temperature zones 305, hot zones 312, the corereaction zone/mixing zone 304 and the reaction chamber outer wall 303,the reactor inlet wall 307 and the location of the plasma torch(es) 308.The concentrated plasma 312 is also shown in FIG. 2. The chamber alsocomprises a frustum-shaped portion. The recirculation path 315 of gasesis caused by the differential in temperatures, pressures and velocitiesof the central region 304 and the boundary regions 305.

FIG. 3 shows a top view of the area of the refinement chamber where theair entrance ports 301 are located.

FIG. 4A-4B shows contours of the gas temperatures and streamlines of airflow along with their temperatures for one embodiment of the system. Thecontours show the core reaction zone/mixing zone 304 and the peripheralsyngas flow zone 306 and their differentiation from each other in thereactor.

FIGS. 5A-5B illustrates a top view and side view of one embodiment,showing a multitude of air entrance ports 301, located tangentially tothe refinement chamber. The reactor inlet wall 307 is also shown in thefigure. Chamber 303 and plasma torch arrangement are the same asdepicted in FIG. 2.

FIGS. 6A-6B show the temperature contours from the top view of theembodiment of FIG. 5. The cross-section is located at the entrance ofthe reactor. FIG. 6A-6B also shows the hot region zone(s) 312 and thecold region zone(s) 313 at two different cross-sections locations in thereactor. The location of FIG. 6A is upstream of the location of FIG. 6B.

FIGS. 7A and 7B show a lateral view and a top view of a third embodimentof the refinement chamber entrance where the air is injected axiallyinto the vessel through air entrance port 301, while the raw syngas isinjected though the tangential syngas entrance port 309.

FIG. 8 shows the model results for gas flow streams for the refinementchamber entrance design depicted in FIGS. 7A and 7B. It shows thedistinct separation between the core reaction zone/mixing region 304 andthe peripheral syngas flow 306.

FIG. 9 shows the temperature distribution for the refinement chamberentrance design depicted in FIGS. 7A and 7B. The distinct temperaturezones are visible in the picture along with the distinct difference intemperatures between the core reaction zone/mixing region 304 and theperipheral syngas flow 306.

FIG. 10 shows the location of the concentrated plasma 314 in therefinement chamber for the refinement chamber entrance design depictedin FIGS. 7A and 7B. The plasma is injected at the edge of the wall intothe gas flow path in this design i.e., the plasma torches are notprotruding into the reaction chamber. The plasma torches 308 are locatedas shown in the figure.

FIG. 11 shows the plasma mass fraction for the embodiment depicted inFIG. 10. The figure shows the distribution of plasma in the gas streamand indicates the location of the concentrated plasma 314.

FIG. 12 shows the flow velocities and distribution of the reactantmixture inside the reactor for a simple refinement chamber entrancedesign, which lacks a frustum shaped entrance portion, in a fourthembodiment.

FIG. 13 shows the plasma concentrations associated with operating thedesign shown in FIG. 12. The drawing shows the location of plasmaspecies present in the mixture within the reactor, using grayscaleshading. The concentrated plasma 314, hot region 312 and cold region 313are seen in the figure.

FIG. 14 shows the flow velocities and distribution for a refinementchamber entrance design similar to the one in FIG. 12, but in thepresence of a frustum shaped entrance portion. The plasma entranceslocation in this design is in the frustum shaped portion, protrudingpast the inner reactor walls.

FIG. 15 shows a view of temperature profiles of the design shown in FIG.7.

FIG. 16 shows plasma entrances that are located horizontally offset fromeach other. In the figure the plasma torches 308 and the concentratedplasma 314 are shown.

DETAILED DESCRIPTION Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used herein, the term “raw syngas” means, generally, a gas generatedduring the gasification process that has not been treated.

As used herein, the term “tar” means high molecular weight hydrocarbonswhich are generally defined as the downstream condensable hydrocarboncomponent in the product gas.

The term “process additives” as used herein, includes any compound thatcan facilitate the partial oxidation of syngas and includes air, O₂,enriched air, steam, CO₂, O₃, H₂O₂, H₂S and combinations thereof.

Overview

This invention provides a system and method for treating raw syngascomprising tar. The system comprises a refining chamber comprising oneor more inlets for raw syngas configured to provide at least two flowzones including a central zone where syngas and air/process additivesflow in a swirling pattern for mixing and combustion; and at least oneperipheral zone that forms a boundary layer of a buffering flow alongthe reactor walls. The system further includes one or more plasmatorches that inject plasma into the central zone. The system is furtherconfigured, such that flow patterns are created in a recirculation zoneto promote mixing between the high temperature products at the corereaction zone and the buffering layer to facilitate complete processing.The system is configured such that in the central zone, syngas andair/process additives mixture is ignited in close proximity to theplasma arc.

The invention further provides a method for treatment of raw syngasincluding tars that comprises mixing the syngas and air/processadditives in a central syngas flow zone, in a swirling pattern forcombustion, with the simultaneous injection of plasma-generatedradicals, electrons and ions into this central syngas flow zone;recirculating a peripheral syngas stream into the core reactionzone/mixing zone created by the combustion of the centrally injectedsyngas with process air/additives, with the simultaneous injection ofplasma-generated radicals, electrons and ions into said central syngasflow zone; creating a stable flame in a reactor comprising a richfuel:air ratio, to facilitate the plasma catalysis of the raw syngas andthe breakdown of tars into lower hydrocarbons and igniting thenear-stoichiometric or oxidising mixture in the central zone, where thesyngas, process additives and plasma come into contact with each other.

In some embodiments, the method and/or system are configured to maximizetar conversion and energy density of the product syngas while optionallyminimizing parasitic power consumption and/or maintenance down-time.

The system is configured to create various zones within the reactionchamber including a zone configured to optimize the conversion of tar byexposure to plasma and at least one zone(s) to shield the reactor wallsfrom being exposed to the high temperature plasma at the reactors' corereaction zone and the reacting species that causes corrosion to thereactor walls.

In some embodiments, this multi-zone system is configured to allow forreactor walls that withstand lower operating temperatures of plasma(+800° C.).

In the present invention, preheated-air/syngas/plasma are mixed toaccomplish multiple objectives; which include allowing part of the rawsyngas to be oxidized, thus providing heat to facilitate refining therest of the raw syngas. Another objective accomplished by this gasfeeding method is to create a recirculation zone that eventuallycombines with the buffering layer into the core reaction zone of thereactor for gas reformulation, once it has served its purpose ofbuffering the reactor walls adjacent to the high temperature corereaction zone of the reactor. Plasma is added to the syngas in such away that it reforms the syngas that wasn't completely oxidized; it alsohelps maintain the flame in the center of the reactor, where thereaction mechanisms shift from oxidizing to reducing.

In some embodiments, the mixture of air and syngas in the refinementchamber is made sub-stoichiometric to maximize tar conversion reactions,while minimizing the use of syngas as heating fuel.

Temperatures of +800° C. are required to breakdown some of the heaviertar molecules into the desired gaseous lower molecular weighthydrocarbons. The elevated temperatures in the refinement chamber can beachieved by a balanced combination of the two following methods:

-   -   1. Pre-heating the air being fed into the refinement chamber.        -   The advantage of this method is that waste heat from a            downstream process is recycled by pre-heating the air,            thereby reducing the requirement for an external energy            source or the requirement for further consumption of            hydrogen and CO. This helps maximize the overall energy            efficiency of process. The disadvantage of using air is            that, thermal energy from combustion of air and syngas, used            to increase the syngas temperature, is now used to raise the            air temperature which is mainly nitrogen, an inert in the            refining process. This extra combustion would result in less            heating value from the resulting refined syngas and would            reduce the efficiency of the process. The nitrogen present            in the air has an added disadvantage of also diluting the            syngas in the reaction chamber and consequently further            reduces the lower heating value (LHV) of the refined syngas.            A reduced LHV of the syngas is undesirable.    -   2. Using the plasma torches in the refinement chamber to inject        hot, reactive, plasma gases into the reactant mixture.        -   The main advantage of the plasma torch is the highly            reactive radicals and electrons it produces, which in            combination with the combustion-generated ions provide for            an effective tar conversion system. Going beyond the use of            the plasma as a reaction catalyst, its use as a heat source            has the main disadvantage of requiring an external power            source i.e., it consumes electricity, which increases the            parasitic power losses within the process-reducing the            electrical efficiency of the process. The advantage of this            method is that it does not dilute the syngas-air reactant            mixture.

Methods 1, 2 or a combination of methods 1 and 2 in the operation of arefinement chamber, are utilized to achieve an optimal balance forproviding thermal energy to the reactants.

The design parameters of the refinement system can be adjusted toachieve desired outcomes (tar conversion or similar objective) for anyspecific process volumetric flow, component concentration in thefeedstock, process temperature, feedstock residence time or otherprocess parameters. The key design parameters that can be adjusted are:

-   -   1. Ratio of the major and minor fuel (raw syngas) stream split        being fed into the reactor. The minor stream (central) can be        from 5% to 50% of the main, raw syngas feed stream with the        balance being the major stream (peripheral).    -   2. The amount and temperature of air fed into the system can        range from 40% to 100% of the volume of the raw syngas entering        the system at a temperature ranging from ambient to 800° C.    -   3. Location, position, power and type of the plasma torches.

The ratio of the flow stream split being fed into the reactor determinesthe size and location of the boundary layer and allows accommodation ofraw syngas with different lower heating values (LHV). The amount andtemperature of air fed into the system allows control of the oxidationpotential of the reactor and allows accommodation of various processconditions and feedstock compositions. The location, position and powerof the plasma torches help in defining the shape and location of theplasma regime within the reactor. For majority of process conditions,the location of the torch(es) will be such that the high energy plasmazone coincides with the oxidation zone in order to take advantage of thesynergies of the two phenomena.

The three aforementioned parameters can be optimized for a wide range ofprocess conditions with feedstock of various compositions to achieve:

-   -   A distinct lower temperature boundary layer that protects        exposure of the walls of the reactor from the high temperatures        that exist in the core reaction zone of the reactor.    -   A plasma gasification reactor that can self-sustain a stable        flame in its core reaction zone, even though the average        air-fuel mixture ratio is not stoichiometric.    -   An economical refinement chamber that maximizes the LHV and        overall usable energy flux of the process raw syngas.

DETAILED DESCRIPTION

FIG. 1 illustrates a general diagram of one embodiment of a refinementsystem showing the raw syngas input 200 and the raw syngas injectedalong the internal periphery of the reactor chamber 800, the processair/additive input 300, the plasma application 400 and the raw syngas,air and plasma mixing zone 600, the reactor body 500 and the processedsyngas product 700.

In accordance with this embodiment, the reactor for refining syngascomprises one or more inlets configured to promote at least two flowzones including a central zone and a peripheral zone, within thereactor. The flow zones can be accomplished by the shape and geometry ofinlet; for example a split of inlet flow into two equal sub-streams canbe accomplished by the inlet being internally divided into two sectionsof equal cross-sectional areas. In the central zone, anear-stoichiometric or oxidising mixture of syngas and air/processadditives flows in a swirling pattern as a flame stabilization strategy;in the peripheral zone, a boundary layer of syngas provides a bufferingflow along the reactor walls protecting the reactor wall from beingexposed to temperatures approaching its melting point and reactingspecies that causes corrosion to the reactor walls. This boundaryprotection layer is important from a thermal and subsequently from aneconomic standpoint, because it dictates the decision on the type ofmaterial that is used to construct/line the walls/body of the reactor. Areactor that is designed for a higher temperature will costsignificantly more than one designed for a lower operating temperaturedue to the cost difference in the materials used in its construction.The reactor is designed such that the fluid dynamics therein, promoteeventual migration of the gases which once formed the boundary layerinto the central zone—this is achieved by the pressure differentialbetween the central zone and the boundary layer achieved in turn byvelocity differences between the regions. Fresh raw syngas now forms anew buffering layer, while the previous buffering layer moves to thecore reaction zone of the reactor and is exposed to the tar conversionprocess before exiting the reactor. The location of plasma injection isoptimized, so plasma gets entrained in the recirculating mixture,thereby facilitating the desired conversion reaction therein andmaximizing the conversion efficiency of the reactor.

The number of flow zones within the reactor is related to the number ofdistinct temperature zones within the reactor, which can be two or morefor any given design.

The near-stoichiometric or oxidising mixture is ignited in the centralzone (mixing region), where the syngas, air and plasma come into contactwith each other, concurrently, at the entrance to the reaction chamber.This mixing region allows the achievement of a stable flame andconsistent temperatures in a reactor comprising an overall rich fuel:airratio, thereby facilitating predictable plasma catalysis of the rawsyngas and the breakdown of tars into lower hydrocarbons, hydrogen andcarbon monoxide. The percent composition of tars in the product of theprocess is of the utmost consideration, which qualifies awaste-to-energy process for certain applications while excluding it fromothers. Another function of the zones in the reactor are to protect theinternal walls of the reactor from the high temperatures (+800° C.) atthe core reaction zone of the reactor and the reacting species thatcauses corrosion to the reactor walls, by limiting the availability ofair/oxygen at the boundary region, directing it to the core reactionzone of the reactor, resulting in lower temperatures at the bufferinglayers.

The present invention can be implemented in various reactor geometries,each of which can be optimized to specific process conditions andobjectives i.e., the process conditions dictate the optimum reactorgeometry for a given set of outcomes.

In the embodiment shown in FIG. 2, the minor stream is routed throughthe central syngas flow zone 302 in direction to a core reactionzone/mixing zone 304, while the major stream of the syngas flow isintroduced along the perimeter of the chamber which forms the peripheralsyngas flow zone 306. The central syngas flow zone 302 is combined withthe incoming process air, fed into process air/additive inlet ports 301leading to produce a near-stoichiometric or oxidising combustiblesyngas-air mixture in a core reaction zone/mixing zone 304, in which themixture is ignited when it arrives in the vicinity of the plasmatorch(es) 308. In the peripheral syngas flow zone 306, a boundary layerof syngas in the low temperature zone 305 (exaggerated for clarity, inFIG. 2) provides a buffering flow along the reaction chamber outer wall303 protecting it from the high temperatures in the core reactionzone/mixing zone 304 and the reacting species that causes corrosion tothe reactor walls, before being pulled into the combustion zone furtherdownstream of the plasma torches.

In this embodiment, the air introduction is composed of two entry ports301, located at opposite sides of the reactor (FIG. 3) on a horizontalplane to each other. The pre-heated air streams are introducedtangentially through air inlet ports 301, which create a swirling flowpattern in the air as it enters the reaction chamber.

FIGS. 4A and 4B show contours of static temperature within anoperational refinement chamber utilizing this design and the splittingof the syngas stream between two zones: central syngas flow zone 302 andperipheral syngas flow zone 306. The swirling motion in the input airstream facilitated by one or more air entrance port(s) 301 creates acore reaction zone/mixing zone 304 within the reactor, in the vicinityof the plasma torches 308, providing a near-stoichiometric or oxidisingsyngas-air mixture. The result is a stable flame and recirculation inthe refinement chamber region and an acceptable tar conversion reaction,minimizing the tar content in the product gases.

This modification of the entrance along with the resulting flow lines isshown in FIG. 14. As shown in the resultant temperature distribution ofFIG. 15, the design allows a gradual transition of the reactant fluidsfrom the input into the reactor via a frustum-shaped portion of thereactor thereby providing a uniform temperature profile, a hot plasmaregion in the core reaction zone of the reactor, reducing erosion of theinternal walls of the reactor due to trapped plasma species.

From a thermal analysis standpoint, the temperature profile of thereactors is divided into at least two distinct temperature zonesincluding a core reaction zone and a boundary zone(s). Each of theseserves a specific purpose. The core reaction zone can be designed to bethe hottest zone in the reactor (FIG. 15) and allows for a stable flamein an otherwise rich fuel:air mixture. This zone is also where theimportant function of high temperature tar-breakdown occurs. The coolertemperature zone(s) are, in this instance designed to be along the wallsof the reactor. The critical function of these zones is to protect thereactor walls from exposure to extreme high temperature (such as thosein the core reaction zone of the reactor) and from the reacting speciesintroduced by the plasma that could cause corrosion of the reactorwalls. If the wall temperature is kept lower than the core reaction zonetemperature, it extends the usable lifetime of the reactor by reducingthermal breakdown of its walls. It also reduces the amount of hightemperature resistant (typically ceramic) material applied to theinternal walls of the reactor, thereby reducing its cost and processdowntime for repair/replacement of the high temperature resistantmaterial. The reactor is designed such that the fluid dynamics therein,promote eventual migration of the gases which once formed the boundarylayer, into the central zone. Fresh raw syngas now forms a new bufferinglayer, while the previous buffering layer moves to the core reactionzone of the reactor and is exposed to the tar conversion process beforeexiting the reactor. The location of plasma injection is optimized, soplasma gets entrained in the recirculating mixture, thereby facilitatingthe desired conversion reaction therein and maximizing the conversionefficiency of the reactor.

TABLE 1 Tar conversion performance for actual operation of theembodiment of FIG. 2 is shown below: Total Tar Concentrations Conversion(mg Tar/Nm³ of raw syngas) Achieved Test # At Inlet At Outlet % 1 40,747mg 6,897 mg 83% 2 50,191 mg 3,040 mg 93% 3 57,675 mg 5,708 mg 90%

In an alternative embodiment, the channels for air protruding into thevessel are replaced with a plurality of external, air entrance ports 301(FIG. 5) allowing a traverse injection of process air into syngas. In anexample with 4 air entrance ports 301 (FIG. 5), hot air is injectedtangentially into the reactor in a traverse direction to the syngasflow, which creates a swirling flow pattern in the resulting air-syngasmixture, enhancing mixing.

The flame created by the air injection is stabilized by the radicalsprovided by the flame created from each adjacent air jet (FIG. 5). Torchgases are injected as close as possible to the reaction zone to boostthe concentration of radicals and increase heating rate as well asmaximize the temperature to facilitate tar conversion. FIGS. 6A and 6B,show examples from Computational Fluid Dynamics (CFD) simulationsshowing temperature distribution, at the plane of the air injection(FIG. 6A) and at a plane approximately 5-6 inches below (FIG. 6B) theplane of air injection. The location of the plasma entrance (torchlocation) can be varied during the design of the refinement chamberentrance to optimize the performance of the apparatus based on specificraw syngas conditions and desired outcomes.

In an alternative embodiment of the invention, air is fed into thereaction chamber vertically down a central axis, while the raw syngas isrouted through a raw syngas feed port 309. As a result a swirling flowpattern is induced in the syngas as it enters the reaction chamber. Inthe reaction chamber the air and swirling syngas come into contact withthermal plasma provided by one or more plasma torches located in theflow path at the entrance to the reactor. The flow streams andtemperature for this embodiment are shown in FIGS. 8 and 9.

The design location of plasma entrance into the refinement chamber canbe optimized for refinement chamber performance. Plasma entrancegeometries can be used to produce different results with reactionchamber performance.

FIG. 16 shows plasma entrances that are located horizontally offset fromeach other. In the figure, the plasma torches 308 and the concentratedplasma 314 are shown.

This embodiment is configured to induce a swirling momentum into themixture entering the reactor, which results in a well-mixed corereaction zone region of the mixture, thereby enhancing plasmadistributions and breaking down tars efficiently. FIG. 10 shows theplasma distribution without a swirling design and FIG. 11 shows it witha swirling reactant mixture.

Alternatively, air input can be via one or more tangential ports. Theresultant, modified flow streams and plasma entrainment is shown in FIG.12 and FIG. 13.

Optionally, the design can be modified by smoothing out the geometricalconditions of the section of the reactor where the reactants enter thereaction chamber.

In various embodiments of the refinement chamber, the raw syngas feed309 can be split into two or more equal or unequal streams before beingfed into the reactor. The number of streams and their respective volumesare a function of the process conditions including, but not limited toinlet temperatures dictated by upstream process conditions, outlettemperatures defined by desired outlet composition, process pressures,feed stock composition, flow rates and the heating value of the streamcomposition.

In one example of the embodiment the streams were split into a minorstream and a major stream (approximately 25% and 75% volumetric ratiosin the test case, to generate a near-stoichiometric or oxidisingfuel:air ratio in the core reaction zone of the reactor) before beingfed into the central syngas flow zone 302 and the peripheral syngas flowzone 306, respectively. In this general embodiment of the invention, theminor stream can be from 5% to 50% of the main, raw syngas feed 309stream with the balance being the major stream.

The invention being thus described, it will be apparent that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be apparent to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A plasma-assisted method for treating raw syngascomprising tars, comprising: (a) mixing a syngas and air/processadditives in a central syngas flow zone, in a swirling pattern forcombustion, with simultaneous injection of plasma-generated radicals,electrons and ions into said central syngas flow zone; (b) recirculatinga peripheral syngas stream into a core reaction zone/mixing zone createdby combustion of centrally injected syngas with process air/additives,with simultaneous injection of plasma-generated radicals, electrons andions into said central syngas flow zone; (c) creating a stable flame ina reactor comprising a rich fuel:air ratio, to facilitate plasmacatalysis of raw syngas and the breakdown of tars into lowerhydrocarbons; and (d) igniting the near-stoichiometric or oxidisingmixture in the core reaction zone, wherein the syngas, air and plasmacome into contact with each other, concurrently, at an entrance to thereaction chamber.
 2. The method of claim 1, wherein the raw syngas feedis split into two equal or unequal volumetric flows: central syngas flowzone and peripheral syngas flow zone respectively, and fed into thereaction chamber.
 3. The method of claim 2, wherein the formation ofzones in the reactor protects the internal walls of the reactor fromhigh temperatures.
 4. The method of claim 2, wherein the formation ofzones in the reactor protects the walls against corrosion caused by thereacting species.
 5. The method of claim 2, wherein the formation ofzones in the reactor limits the amount of air/oxygen at the boundaryregion directing it to the core reaction zone of the reactor.
 6. Themethod of claim 5, wherein limiting the amount of air/oxygen at theboundary region results in lowering temperatures at the bufferinglayers.
 7. The method of claim 6, wherein the buffering layer combineswith the recirculation zone into the core reaction zone of the reactor.8. The method of claim 1, wherein the air/process additives are injectedaxially into the vessel while the raw syngas is injected though thetangential port.
 9. The method of claim 1, wherein the method isimplemented using a plasma-assisted system for treating raw syngascomprising tars, where the system comprises: a refining chamber forrefining syngas comprising one or more inlets configured to promote atleast two flow zones: a core reaction zone where syngas and air/processadditives flow in a swirling pattern for mixing and combustion in thehigh temperature central syngas flow zone; at least one peripheral zonewithin the reactor which forms a boundary layer of a buffering flowalong the reactor walls; one or more plasma torches that inject plasmainto the core reaction zone; and air/process additive injection inputsconfigured to create a recirculation zone thereby promoting mixingbetween high temperature products at the core reaction zone of thevessel and the buffering layer, wherein in the core reaction zone,syngas and air/process additives mixture are ignited in close proximityto the plasma arc, coming into contact with each other, concurrently, atthe entrance to the reaction chamber.